Apparatus and method for elutriating and measuring fine solid particles



3.269 OD FOR ELUTRIATING AND MEASURING Aug. 30, 1966 G. w. MONK APPARATUS AND METH FINE SOLID PARTICLES Filed Dec.

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INVENTOR ATTORNEYS.

United States Patent lice 3,269,189 APPARATUS AND METHOD FOR ELUTRIATING AND MEASURING FliNE SOLID PARTICLES Gaines W. Monk, Alexandria, Va., assignor to the United States of America as represented by the Secretary of the Army Filed Dec. 18, 1964, Ser. No. 420,253 8 Claims. (Cl. 73-432) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a method and apparatus for separating dust particles into various classifications of size in a vacuum chamber.

In the drawing:

FIG. 1 is a cross section through one form of the invention; and

FIG. 2 is a cross section through a modification.

A lightweight cylinder 1, of aluminum foil or such, is attached to an electric vibrator 2, such as a radio-type sound generating speaker. A.C. or pulsed DC. current is supplied to vibrator 2 through electrical leads 3. Powder or dust particles to be analyzed are placed in cylinder 1 on the vibrator as at 4.

Valve 5 is adjusted for a desired flow rate of air or other gas into powder 4 through conduit 7 while gage 6 indicates the pressure of the gas introduced through conduit 7.

The pressure in hell jar 8 may be measured by a gage connected through conduit 9. The pressure may be decreased to obtain a high vacuum by connecting a vacuum pump to conduit 10. The bottom of bell jar 8 is closed by sealed contact with plate 11. The capacity of vacuum-producing equipment 20 is large enough to continuously remove the gas introduced through 7 while maintaining a high vacuum inside of bell jar. 8

A lightweight disc 12 serves as a collector for powder or dust particles rising through tube 1 and falling in the evacuated chamber 8. A weight balance 13 comprises a weight 14, supporting wires or filaments 15, 15 and an indicator 16 with a scale of indicia 17 therebehind.

Operation Powder to be tested is placed at the bottom of cylinder 1 as illustrated at 4. The bell jar 8 is sealingly placed over the apparatus and a high vacuum is drawn through outlet 10 by vacuum pump 20. Electric vibrator 2 is placed in operation and valve 5 is opened to admit gas into powder 4 to thereby agitate and lift the powder through cylinder 1. The viscous drag on the particles caused by the gas rising in cylinder 1 lifts the lightweight, or low density, particles up and out of the cylinder.

At a predetermined low rate of gas flow, only very lightweight particles, or those of low density, will be lifted by the upward flowing gas in cylinder 1. As soon as these particles are up and over the edge of cylinder 1 they drop like lead in the high vacuum existing in bell jar 8 outside of cylinder 1. Thus, the particles of a certain very small size, or those of a low density, are soon deposited on disc 12. The quantity of such particles is determined by the operator and recorded as indicated by the position of pointer 16 on scale 17. Larger or more dense particles remain in the pile of particles at 4.

Valve 5 is opened further and the rate of flow of gas into powder 4 and up through cylinder 1 is increased. Then, heavier or more dense particles are raised through cylinder 1 and deposited on disc 12. Again the quantity of such size particles is checked. And again the steps are repeated until all of the particles of the various classifications are determined and recorded by the operator.

3,269,189 Patented August 30, 1966 In FIG. 2 a modification of the particle collecting and classifying apparatus is disclosed. Instead of collector disc 12 and weight balance 13, concentric cup receivers 21, 22 may be used. Heavier or dense particles will fall in cup 21 as at 23 and lighter or less dense particles will carry over into cup 22 and will fall as at 24. Particles above a certain weight or density will be too heavy or dense to be carried out of cylinder 1. Therefore, the apparatus illustrated will yield three classifications of particles.

If desired, a greater number of cups may be used to obtain a wider classification of the particles. Alternatively, the particles at 23, 24 may be removed, their quantities recorded, and gas flow in through conduit 7 may then be increased. Then, larger particles will be lifted out of cylinder 1 and deposited at 23, 24, thus yielding further classifications.

If the gas is at such a low pressure that the viscous drag is negligible the theory indicates that the maximum diameter of a spherical particle that can be carried out of any such tube is given approximately by where: D is the diameter of the sphere in microns; p is the atmospheric pressure in millimeters; V is the volume rate in cm. per sec. measured at atmospheric pressure of the gas entering the tube 7, d is density of the spheres in grams/cm. and A is the cross-sectional area of the tube 1.

It is seen then the volume rate determines the size of particle that is carried onto the pan in a given system.

The pumping system must be fast enough to maintain the pressure so low that the simple relation given in (1) holds for the particles of interest. This is about 10 mm. for micron particles to 1 mm. for micron particles of unit density. The unit will work at higher pressures, but the simple relation does not hold and the calibration is not independent of the pressure.

For optimum results the vacuum in chamber 8 should be at a high level so that the particles will drop decisively or plummet downwardly after leaving cylinder 1 and will not be affected appreciably by eddy currents or other stray currents, or by collision with air particles in bell jar 8.

I claim:

1. The method of separating dust particles according to size or density which comprises: placing the dust at the closed bottom of a vertical tubular member and inside of a chamber; drawing a vacuum in said chamber; agitating said dust; introducing a stream of gas at a predetermined rate into said vertical tubular member adjacent to the dust to thereby raise the smaller or less dense particles to and over the top of said vertical tubular member whereby said particles will plummet down in the vacuum around said tubular member; and collect ing the separated particles.

2. The method of claim 1 and; as a further step in the method of separating particles, introducing said gas at a more rapid rate than in the first step, thereby raising larger or more dense particles to and over the top of said vertical tubular member to thereby separate such particles; and collecting the langer or more dense particles.

3. Apparatus for separating dust particles comprising: an enclosed chamber; material support means in said chamber to support a quantity of dust particles; means to introduce a gas into said quantity of dust particles; means to regulate the rate of fiow of gas into said quantity of dust particles to separate out lighter or less dense particles at low gas flow or heavier or more dense particles at higher gas flow; means to determine the quantity 3 of dust particles separated out from said quantity; and means to produce a vacuum in said chamber whereby said dust particles will fall quickly after being separated out from said quantity.

4. Apparatus as in claim 3 wherein said material support means comprises vibrating means to vibrate said quantity of dust particles.

5. Apparatus as in claim 4 wherein said vibrating means comprises an electromagnetically driven vibrating diaphragm.

6. Apparatus as in claim 5 wherein said material support means further comprises a cylindrical member above said electromagnetically driven diaphragm whereby vibrations from said diaphragm and gas introduced into said quantity of dust particles lift the lighter weight or less dense particles up and over the open top edge of said cylindricallmember to thereby separate such particles from the heavier or more dense particles.

7. Apparatus as in claim 6 wherein said means to determine the quantity of dust particles separated out comprises a disc surrounding said cylindrical member for the separated particles to collect on, and means to register the mass or Weight of particles s0 separated.

8. Apparatus as in claim 6 wherein said means to determine the quantity of dust particles separated out comprises a cylindrical cup around said cylindrical member to receive the separated dust particles as they pass over the top edge of said cylindrical member and plummet downwardly.

References Cited by the Examiner UNITED STATES PATENTS FRANK W. LUTTER, Primary Examiner. 

3. APPARATUS FOR SEPARATING DUST PARTICLES COMPRISING: AN ENCLOSE CHAMBER; MATERIAL SUPPORT MEANS IN SAID CHAMBER TO SUPPORT A QUANTITY OF DUST PARTICLES; MEANS TO INTRODUCE A GAS INTO SAID QUANTITY OF DUST PARTICLES; MEANS TO REGULATE THE RATE OF FLOW OF GAS INTO SAID QUANTITY OF DUST PARTICLES TO SEPARATE OUT LIGHTER OR LESS DENSE PARTICLES AT LOW GAS FLOW OR HEAVIER OR MORE DENSE PARTICLES AT HIGHER GAS FLOW; MEANS TO DETERMINE THE QUANTITY OF DUST PARTICLES SEPARATED OUT FROM SAID QUANTITY; AND MEANS TO PRODUCE A VACUUM IN SAID CHAMBER WHEREBY SAID DUST PARTICLES WILL FALL QUICKLY AFTER BEING SEPARATED OUT FROM SAID QUANTITY. 